This text ends in an "INA clause" which is a structure-signaling word that
governs the verb that follows it in the subjunctive. I think this is what
the author of your commentary is trying to say. Since the "INA clause"
governs the verb in the subjunctive the verb that follows it "has to be
(forced) in the subjunctive". It also sounds like the commentary is a bad
English translation of an original German text.